Method for the prevention of barnacle attacks

ABSTRACT

A method for impregnating wooden items, in particular poles situated in marine environment against attack from Teredo, where the method includes the following steps: d) a hole is formed in parallel with the fibre orientation of the wood, e) the hole is then filled with an impregnating agent containing a biodegradable chelating agent, f) after which the hole is closed.

The present invention concerns a method for impregnating wooden itemsagainst attacks from Teredo, particularly poles situated in marineenvironment.

Teredo is the Latin term for the family of shipworms that mainly live insalty water and mainly live off cellulose, which e.g. is found in wood.Shipworm is a long, worm-shaped bivalve, the shell of which onlycovering some of the front end of the animal.

Shipworms are active in the entire submerged length of the pole, i.e.from over the bottom to the surface zone. Attack by shipworms often onlyappears as small holes into which the larvae have disappeared. In thefirst year, shipworms are male, then changing to female. Reproductionoccurs by male and female worms releasing semen and eggs to the water,after which fertilisation and hatching occurs freely in the water. Whenthe larva is hatched, it seeks out a wooden item in the water, includingpoles and the like. The larva bores into the e.g. pole and lines thepassage with a thin layer of lime. In the larva stadium, the shipwormlarva is feeding mainly on cellulose fibres from the pole in which ithas been born while at the same time eating and growing so that thedestructive effect on the pole becomes more and more comprehensive. Thusit is difficult to judge to which extent a given pole is attacked byTeredo.

In order for the Teredo family of shipworms to live, a certain watertemperature, a certain saltiness, and wood must be present. In thewarmer areas of the Middle Ocean, shipworm attacks have been widespreadfor a long time, and in recent years the attacks have also spread toDanish waters.

In order to counteract and curb attacks from Teredo, one may use exoticwood species for one's poles, including e.g. cypress wood, jarrah wood,turpentine wood. These and a few other types of wood are naturallyresistant against Teredo attacks, but are very rare species of wood aswell as they are very expensive. Degrading of the wood cannot beavoided, but the service life of the pole can be prolonged.

Another way of preventing Teredo attacks is to impregnate with chemicalmeans. Since most chemical agents are environmentally hazardous, thereis a desire to reduce the use of environmentally harmful agents as theseare leached out into the sea water and thereby have negative effect onthe marine environment around the pole.

A third method is to use mechanical or chemical barriers. A kind ofmechanical barrier is to coat the pole with a copper layer or a concretelayer. This is a costly and cumbersome method, which in many cases makesit advantageous from an economic point of view to let the pole standuntreated, and, when the pole is degraded by Teredo attacks, tosubstitute it with a fresh pole.

A fourth method for preventing Teredo attacks is to coat the poleexternally with a chemical barrier, e.g. in the form of a plastic filmimpregnated with a chemical material. This method has the samedisadvantages as the chemical impregnation of the pole as often thereare released very poisonous substances to the surrounding marineenvironment with associated harmful effects.

Thus there exists a need for producing a cheap and secure impregnationof wooden poles, whereby it is ensured in an environmentally safe waythat the poles are safe-guarded against attacks from Teredo.

This is provided according to the invention by a method which ispeculiar in comprising the following steps:

-   -   a) a hole is formed in parallel with the fibre orientation of        the wood;    -   b) the hole is then filled with an impregnating agent containing        a biodegradable chelating agent;    -   c) after which the hole is closed.

With the method according to the invention it has surprisingly appearedthat the impregnation agent has a good ability to penetrate and disperseout in the wood, and further that the Teredo larvae and worms cannotlive when impregnating agent is present in the pores of the wood. Thusthere is produced a very efficient protection against shipworm attacks,as well as the method is relatively simple to implement, and furthermorecontinuous maintenance is easily performed by replenishing impregnationliquid in the holes. As furthermore the impregnating liquid is notenvironmentally hazardous, the new impregnating method therefore has noinfluence on the marine environment around the pole.

In a preferred embodiment, the impregnation agent contains chelatingagent ranging from 1% to 25%, more preferably 5% to 15%.

Thus there is provided a method which is both cheaper and more rapidthan the previously known, as well as it is environmentally neutralcompared with the marine environment around the pole.

In order to amplify the ingress of the impregnating agent into the wood,the impregnating agent may be filled into the hole under pressure,preferably with a pressure between 10 and 200 bar. The applied pressureenhances distribution of the impregnation agent in the wood tissue andthereby the impregnation process. However, in this connection, it is tobe underlined that the impregnation liquid will disperse in the woodtissue also in the embodiments of the method where pressure is notapplied. This is due to the composition of the impregnation agent whichhas a relatively low surface tension due to the chemical composition.

In the embodiments where pressure on the liquid in the pole is wanted tobe applied simultaneously with supplying impregnating agent, this isdone by a pipe being placed inside the hole, the pipe being providedwith a screw thread for connecting an impregnation agent supply hose.Furthermore, the pipe has the property that it has an outer diameterwhich is slightly greater than the inner diameter in the hole, wherebythe pipe is fixed in the wooden item. Then the supply hose may beconnected to a pressurised vessel in which the impregnating agent isprovided and then supplied to the wooden item via the supply hose andthe pipe.

In a preferred embodiment of the invention, the entire hole in thewooden item in parallel with the fibre orientation is from 1200 mm to2000 mm deep, and that the hole diameter is from 25 mm to 50 mm,preferably from 30 to 45 mm, and more preferably 38 mm, in a firstsection closest to an end face at a depth from 0 to 750 mm, and that thehole diameter is from 10 mm to 25 mm, preferably 15 mm to 20 mm, andmore preferably 19 mm, in the remaining section of the depth of thehole.

These dimensions have appeared to be optimal on far the most of thekinds of wooden items used for mooring posts and bridge posts, as it isensured in this way that enough impregnating agent is placed in the holein the wooden item at the same time as the liquid in disposed deeplyenough in the wooden item so that it may penetrate out into the entirepole and hereby protect it efficiently against attack from Teredo.

Besides the mix of water and chelating agents, impregnating agentsconsisting of water, alcohol and soda, citric acid and similar productshave appeared effective against shipworms and usable by the methodaccording to the invention.

In a preferred embodiment of the invention is used an impregnation agentcontaining from 1% to 25% biodegradable chelating agent. The chelatingagent ensures that the impregnating agent is not so easily washed out ofthe wood but also that an anti-Teredo environment is created.

Where treating very large wooden items, e.g. mooring posts with a largediameter, in a preferred embodiment of the invention there may beprovided a plurality of holes parallel with the fibre direction in theend face of each wooden item. Hereby the distance which the impregnatingliquid is to penetrate the wood becomes less, whereby a more optimaltreatment of the wooden item is ensured so that the impregnation liquidbecomes evenly distributed in the entire wooden item.

In a preferred embodiment, the method is particularly applicable onwooden poles, including bridge or mooring posts placed in salty water.There are many of these posts in normal harbours, and particularly inmarinas wooden poles are used in great numbers for the construction oflanding-stages and mooring posts.

In a further, preferred embodiment of the method according to theinvention, on each pole is to be filled with 10 to 50 litresimpregnating liquid, preferably 20 to 40 litres, and more preferably 30litres impregnating agent in each hole. Even though the immediate sizeof the hole does not allow filling of the total amount of impregnatingliquid at once, the filling should be continued until the aboveindicated amount has been absorbed in the pole.

The filling may possibly occur by the top of the hole being fitted witha reservoir, which contains an amount of impregnating agent, so that, asthe impregnating agent is dispersed in the wood pole, the level in thereservoir drops. Thereby it is easy to check when the impregnating agentis to be replenished as well as checking on the filled amount may easilybe updated.

In some cases the poles to be treated are erected so that they form asheet piling, and in some case there is no access to the wood postsabove the water level. Under these conditions, by using the invention itis possible to bore a filling hole in the wood pole under water leveland then to connect a filling stub. The filling stub is connected with ahose or similar to a tank in which impregnating agent is kept underpressure, e.g. 12-20 bar. In the same way as described above, it ishereby possible to impregnated poles which are not accessible over thewater level and/or forming a sheet piling.

Above, the invention has been describe with regard particularly toapplication on poles which are already placed in a marine environment.The impregnating agent and the effect attained thereby is, however, justas applicable in a compregnation process on new poles. This impliessubstantial economic savings, as it is more rational to treat severalpoles at a time than to treat each pole individually on site.

The method will now be explained with reference to the accompanyingdrawing.

FIG. 1 shows a pole with a bored hole.

FIG. 2 shows a drilling device for use in the method.

FIG. 3 shows a pole with pressure equipment.

FIG. 4 shows a finished pole.

FIG. 5 shows a pole with fitted reservoir.

In FIG. 1 is illustrated a mooring post 1 placed in a marine environmentso that the pole is thrust into the bed 2. The pole will typicallyprotrude up over the water level 3, either to form part of a bridgestructure or to be used as mooring post However, in this connection itis to be mentioned that the method according to the invention is notlimited to the mooring posts or posts forming part of bridge structures,but may be used for all kinds of wooden items that are exposed to Teredoattack, i.e. wooden items placed in salty, marine environment.

Between the bed 2 and the water level 3, under given conditions, i.e. agiven water temperature and salinity, there will be risk of attack fromTeredo (pole worm or shipworm).

The invention thus indicates a method for protecting wooden itemsagainst attacks from Teredo. In the pole 1 is formed a hole 4 inparallel with the longitudinal orientation of the fibres. The hole is tobe deep enough to reach down under the water level, i.e. typically 1½ to2 m deep.

In FIG. 2 is shown a tool used for making the hole 4 in the pole 1. Thetool comprises a very long drill 5 corresponding to the depth of thehole, i.e. up to 2 m long. The drill 5 itself is hollow, and an aperture6,7 is provided at both ends of the drill. In the aperture 6 there maybe connected a compressor pumping compressed air down through the drillto the outlet 7. The drill is brought to rotate by means of a drillingmachine 9 connected at the upper end of the drill. During the drillingof the hole 4, compressed air is conducted in through the aperture 6,down through the drill 5 and out through aperture 7, in order thereby toremove and enhance transport of wood chips produced by the drillingprocess up through the hole and out of the pole.

In FIG. 3 is illustrated the succeeding stage of the method according tothe invention, as there is inserted a pipe 10 in the upper part of thehole 4. In the pipe 10, there is a connecting facility for a supply hose11, which is led to a reservoir 12 that possibly may be pressurised. Inthe reservoir 12, the impregnation agent is placed so that theimpregnation agent is conducted through the supply hose into the pipeand thereby into the inner part of the pole. The impregnation agent willdisperse into the wood 13 as illustrated with arrows 14. The hole 4 isoutlined as filled with impregnating agent 15. When the desired amountof impregnating agent has been supplied to the pole, the connection tothe reservoir 12 is disrupted, and supply hose and pipe are then removedfrom the pole.

After finished impregnation, a plug 16 is attached as illustrated inFIG. 4. In the hole 4 there may still stand an amount of impregnatingagent 15 which will disperse into the wood 13 over time. The wood isillustrated in FIG. 4 as being impregnated with impregnating agent 15 by17.

After impregnation, it will be relatively simple to check when theimpregnating liquid is to be replenished, as one just removes the plug16 from the hole 4, whereby access is provided to the hole 4 in theinterior of the pole 1. When the impregnating agent level in the hole 4becomes sufficiently low, more impregnating agent may easily be filledinto the hole.

In an alternative embodiment of the method as illustrated in FIG. 5,supply hose and pressurised reservoir 11,12 have been substituted with atank 18, which is connected with the hole 4, possibly via a pre-fittedpipe 10. In the tank 18, there is provided an amount of impregnatingagent 15 which will be actuated by gravitational force and then dispersein the pole, i.e. the wood as outlined with the arrows 14. When it isdetected that the pole has been supplied a predetermined amount ofimpregnating agent, the tank 18 is removed from the pipe 10, after whichthe pole is finished as illustrated in FIG. 4.

1. A method for impregnating wooden items, particularly poles situatedin a marine environment against attack from Teredo, where the methodincludes the following steps: a) a hole is formed in parallel with thefibre orientation of the wood, b) the hole is then filled with animpregnating agent containing a biodegradable chelating agent, c) afterwhich the hole is closed.
 2. A method according to claim 1, wherein theimpregnating agent contains chelating agent ranging from 1% to 25%, andmore preferably 5% to 15%.
 3. A method according to claim 1, whereinbefore step b) there is inserted a pipe, which pipe is provided at oneend with screw thread for connecting a impregnating agent supply hose.4. A method according to claim 1, wherein the impregnating agent isfilled under pressure, preferably a pressure between 10 bar and 200 bar.5. A method according to claim 1, wherein the entire hole in the woodenitem parallel with the fibre orientation is from 1200 mm to 2000 mmdeep, and that the hole diameter is from 25 mm to 50 mm, preferably from30 to 45 mm, and more preferably 38 mm, in a first section closest to anend face at a depth from 0 to 750 mm, and that the hole diameter is from10 mm to 25 mm, preferably 15 mm to 20 mm, and more preferably 19 mm, inthe remaining section of the depth of the hole.
 6. A method according toclaim 1, wherein a plurality of holes is provided parallel with thefibre orientation at the end face of each wooden item.
 7. A methodaccording to claim 1, characterised wherein the wooden item is a woodenpole, e.g. a bridge post or mooring post placed in salty water.